/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.messaging.core;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.beans.factory.BeanFactoryAware;
import org.springframework.lang.Nullable;
import org.springframework.messaging.MessageChannel;
import org.springframework.util.Assert;

/**
 * An implementation of {@link DestinationResolver} that interprets a destination
 * name as the bean name of a {@link MessageChannel} and looks up the bean in
 * the configured {@link BeanFactory}.
 *
 * @author Mark Fisher
 * @since 4.0
 */
public class BeanFactoryMessageChannelDestinationResolver
        implements DestinationResolver<MessageChannel>, BeanFactoryAware {

    @Nullable
    private BeanFactory beanFactory;


    /**
     * A default constructor that can be used when the resolver itself is configured
     * as a Spring bean and will have the {@code BeanFactory} injected as a result
     * of ing having implemented {@link BeanFactoryAware}.
     */
    public BeanFactoryMessageChannelDestinationResolver() {
    }

    /**
     * A constructor that accepts a {@link BeanFactory} useful if instantiating this
     * resolver manually rather than having it defined as a Spring-managed bean.
     *
     * @param beanFactory the bean factory to perform lookups against
     */
    public BeanFactoryMessageChannelDestinationResolver(BeanFactory beanFactory) {
        Assert.notNull(beanFactory, "beanFactory must not be null");
        this.beanFactory = beanFactory;
    }


    @Override
    public void setBeanFactory(BeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }


    @Override
    public MessageChannel resolveDestination(String name) {
        Assert.state(this.beanFactory != null, "No BeanFactory configured");
        try {
            return this.beanFactory.getBean(name, MessageChannel.class);
        } catch (BeansException ex) {
            throw new DestinationResolutionException(
                    "Failed to find MessageChannel bean with name '" + name + "'", ex);
        }
    }

}
